a) Field of the Invention
The invention is directed to a universal ophthalmic examination device which has, in combination with a central control unit, at least one primary light source in an illumination beam path directed to an object being examined and at least one image recording and evaluating unit for documenting and/or for measuring at least partial areas of the object being examined, and electronically switchable elements for beam path switching.
The invention is further directed to an ophthalmic examination method in which an object to be examined is illuminated and selectively stimulated by an illumination beam path for recording images with light of at least one light source and in which examination results are derived by recording images of the object to be examined and evaluating the images obtained by the image recording.
The invention is applicable in diagnostic systems in which image generation, measurement, stimulation and functional imaging of the eyeground or ocular fundus are component parts of the examination of the human and animal eye. In particular, systems of this type include ophthalmoscopes, mydriatic and non-mydriatic retinal cameras, systems for vascular analysis and measurement of various other quantities of microcirculation, metabolism, circulation time by means of indicator technique, blood velocity (LDV, LDF) and spectrometric data at the fundus that are based on direct or indirect ophthalmoscopy.
b) Description of the Related Art
Known image-generating systems use flash devices or continuous light sources as illumination systems.
While image documentation in flash mode generates high-quality images, the succession in time on individual images per second is limited in terms of technique and also with respect to the light stress for patients. In addition, devices with flash beam paths are cost-intensive and lead to an increase in structural size and weight.
Continuous illumination, on the other hand, enables continuous sequences of image recordings, e.g., in video mode, but the images have only a low geometric resolution and poor image quality because of the light stress limit and the continuous illumination itself.
While stepping up the control of the lamps that are used improves the image quality with reasonable light burden, the flickering of the light that is caused by the inertia of the lamp and is perceptible to the patient leads to corresponding anticipatory attitudes, blinking, squinting and eye movements which again leads to considerable impairment of image quality.
Further, it is known to display stimulated (provoked) topographic measurements in fundus images. By means of functional imaging, as it is called, it can be observed on the basis of the time curve of the response reaction of the retinal vessels how the autoregulation mechanism attempts to eliminate the disturbance (provocation) through changes in vascular diameter.
Apart from stimulation, functional imaging also requires high-quality image generation and measurement; it should also be ensured as far as possible that time allocation is free and that it is possible to change rapidly between image generation, stimulation and measurement. Combination with infrared illumination is useful for reducing the light burden on the patient, e.g., during stimulation with light.
A known device according to EP 1 100 370 B1 is based on the use of functional changes in retinal reflectivity in which light of a stimulating illuminator is blended into the beam path in addition to the continuous illumination to induce a detectable function response signal. The light of the two separate beam paths can be alternately switched or superimposed.
In this arrangement, stimulation is used to change the structure and light-scattering characteristics of determined layers of the retina. Since the biological response is seen in the diffuse reflection of the retinal structures, this device is oriented to the examination of changes in radiation characteristics in that changes in diffuse reflection are compared and documented by generating differential images for two different function states.
Although this offers the advantage that the light from any light sources can be superimposed or alternately switched, it is disadvantageous that stimulation necessitates another device whose light must be brought to the retina on an additional beam path by means of a splitter mirror.
When structures at the ocular fundus are measured for function diagnostic examinations instead of using functional changes in retinal reflectivity, DE 196 48 935 A1 offers a system which is suitable for blood vessels that are visually accessible or can be imaged in some other manner and by which the essential relevant clinical function diagnostic characteristic quantities can be determined and displayed with high reproducibility and minimal stress on the patient. For provocation, flickering light can be provided in a separate beam path and is superimposed on the continuous measurement light. Since the modified flash beam path serves as a separate beam path, there is the disadvantage that high-quality image documentation by means of flash light for functional imaging is discarded.